Elucidation of the oncogenes involved in human breast cancer may have important prognostic and therapeutic implications as is already documented for erbB-2/neu/Her.2. We now seek to investigate the involvement of each of the known erbB family members in a series of human breast Carcinoma cell lines by measuring their protein expression levels, constitutive phosphorylation and physical interactions. We will also study the mechanisms responsible for cooperative transformation between erbB-2 and erbB-3 at a molecular and biochemical level and mechanisms causing coactivation of these receptors in some breast tumors. Recent studies have revealed new oncogenic members of the ras family, TC21 and R-ras, and our preliminary studies demonstrate striking TC21 overexpression in a human breast tumor cell line. We seek to develop further evidence of the involvement of ras-like genes in breast tumors using antibodies which specifically detect their overexpression and PCR-based molecular genetic approaches to search for oncogenic activating mutations. The possibility that these new ras genes may mediate transforming/proliferative signaling by erbB family members will also be explored by determining their ability to cooperate for transformation and increase GTP binding in response to different erbB family receptors. Breast epithelial cell transfectants will be established to test the oncogenic potential of the oncogenes implicated in a relevant experimental model. The knowledge gained should be useful in assessing the efficacy of new therapeutic modalities in breast cancer.